<topic>
	<head>
		<title>ATAN</title>
		<keywords>
			<keyword term="functions, ATAN" />
			<keyword term="mathematical functions, ATAN" />
			<keyword term="ATAN function" />
		</keywords>
		<links>
			<link href="Functions.html">Functions</link>
			<link href="Mathematical Functions.html">Mathematical Functions</link>
		</links>
	</head>
	<body>
		<summary>
			<p>
				A mathematical function that returns the angle, in radians, whose tangent is a specified double expression; also called arctangent.
			</p>
		</summary>

		<syntax>
			<code xml:space="preserve">ATAN (value AS double) RETURNS double</code>
		</syntax>

		<parameters>
			<params>
				<param name="value">
					<p>
						A number representing a tangent.
					</p>
				</param>
			</params>
		</parameters>

		<returns>
			<p>
				An angle, θ, measured in radians, such that <c>-π/2 ≤ θ ≤ π/2</c>,
			</p>
			<p>
				-or-
			</p>
			<p>
				<c>NaN</c> if <c>value</c> equals <c>NaN</c>,
			</p>
			<p>
				-or-
			</p>
			<p>
				<c>-π/2</c> rounded to double precision (-1.5707963267949) if <c>value</c> equals <c>NegativeInfinity</c>,
			</p>
			<p>
				-or-
			</p>
			<p>
				<c>π/2</c> rounded to double precision (1.5707963267949) if <c>value</c> equals <c>PositiveInfinity</c>.
			</p>
		</returns>

		<examples>
			<sampleCode language="NQuery.SQL" xml:space="preserve">SELECT 'The ATAN of the angle -181.01 is: ' + TO_STRING(ATAN(-181.01))
UNION  ALL
SELECT 'The ATAN of the angle 0 is: ' + TO_STRING(ATAN(0))
UNION  ALL
SELECT 'The ATAN of the angle 0.1472738 is: ' + TO_STRING(ATAN(0.1472738))
UNION  ALL
SELECT 'The ATAN of the angle 0.1472738 is: ' + TO_STRING(ATAN(0.1472738))
UNION  ALL
SELECT 'The ATAN of the angle 197.1099392 is: ' + TO_STRING(ATAN(197.1099392))</sampleCode>
		</examples>
	</body>
</topic>
